In the related art, nuclear medicine imaging apparatuses such as a single photon emission computed tomography (SPECT) apparatus or a positron emission computed tomography (PET) apparatus have been known as a medical image diagnosis apparatus capable of performing functional diagnosis in body tissues of a subject.
Specifically, the nuclear medicine imaging apparatus detects a gamma ray emitted from an isotope or a labeled compound selectively received in the body tissues using a detector and reconstructs a nuclear medicine image obtained by portraying a radiation dose distribution of the detected gamma ray.
In recent years, apparatuses such as a PET-CT apparatus or SPECT-CT apparatus are widely used, in which a nuclear medicine imaging apparatus is integrated with an X-ray computed tomography (X-ray CT) apparatus that provides shape information in the body tissues of the subject. For example, a whole-body examination using the PET-CT apparatus is indispensable in tumor diagnosis.
In the SPECT apparatus or the PET apparatus, typically, a successive approximation type image reconstruction method is used unlike an image reconstruction method performed in the X-ray CT apparatus. The successive approximation method is not an analytical method, but highly tolerant to noise in principle. As an example of the successive approximation methods, a maximum likelihood expectation maximization (MLEM) technique and an ordered subset MLEM (OSEM) technique, in which an MLEM algorithm is modified to remarkably reduce a processing time, have been developed.
However, since the image reconstruction method based on the successive approximation takes a long time, examination efficiency using the medical images may be degraded.